Circuit arrangement for at least one electric load of a motor vehicle

ABSTRACT

A circuit arrangement for at least one electric load of a motor vehicle such as a windshield wiper system is disclosed, in which the switching signals of an operating switch of the system are in a coded manner transmitted to a programming unit which a detector with several ranges of detection for the various coded switching signals. The detector has additional ranges of detection for switching signals not associated with particular modes of operation, so that troubles in the system can be recognized by the detector in the programming unit providing for improved system operational reliability.

BACKGROUND OF THE INVENTION

This invention relates to a circuit arrangement for use with at leastone electric accessory load of a motor vehicle.

In modern motor vehicles; the number of electrically operatedaccessories defining electrical loads and the number of modes ofoperation of the various loads in a motor vehicle have been considerablyincreased. For example, typically four modes of operation are providedfor the wiper motor of a motor vehicle windshield cleaning system.Namely one mode of operation is for the parking position run of thewiper motor, one mode of operation for slow wiper speed, one for a fastwiper speed and a so-called intermittent mode of operation in which thewiper motor is stopped for a defined period of time after each windingcycle. To some windshield cleaning systems this delay or interval timeis firmly and invariably predetermined. In other windshield cleaningsystems the interval time can be continuously adjusted through apotentiometer.

This interval time can also be made variable in several steps, wherein,instead of the potentiometer, different fixed resistors are connectedwith a timing element. In a windshield cleaning system of this kindseveral different modes of intermittent operation may be achievedthrough an operating switch. Thus, in a system of this kind theoperating switch has several operating positions for the various modesof operation, wherein the different switching signals of the operatingswitch are conducted to a programming unit which determines the mode ofoperation determined by the operating switch. In today's windshieldcleaning systems an expensive cable with a number of switching signaltransmission paths or leads corresponding to the number of differentmodes of operation is necessary to transmit the switching signal of theoperating switch to the programming unit. It can easily be seen that thecosts for this lead will increase with the number of different modes ofoperation. In order to reduce costs circuit arrangements have beendevised in which different voltage levers corresponding to the variousoperating positions are switched onto a switching signal transmissionpath or lead by the operating switch, and the programming unit has adetector with ranges of detection associated with the different voltagelevels and accordingly determines the mode of operation. A circuitarrangement of this kind which includes only one switching signaltransmission path between the operating switch and the programming unitis, for example, disclosed the German specification No. DE OS 2,944,224.The amount of circuitry between the operating switch and the programmingunit can be reduced considerably by a construction of this kind. It istrue, however, that a circuit arrangement of this kind does not alwaysoperate reliably. For example, if a short-circuit of the switchingsignal transmission path or of the input of the programming unit withone or the other poles of the voltage source occurs a voltage level isprovided at the input of the programming unit which corresponds with avoltage level of one of the modes of operation. Consequently, thewindshield cleaning system can be inadvertently put into operation or aparticular unwanted mode of operation can be switched on. A similarfault can also occur during a changeover of the operating switch fromone mode of operation to another, because during this period of time nodefined potential is switched onto the lead to the programming unit.

SUMMARY OF THE INVENTION

Thus, the present invention is directed to improving the operationalreliability of a circuit arrangement of this kind.

The invention is based on the premise that faulty conditions, e.g.,short-circuits, or such conditions which appear compulsorily, but cannotbe associated with any particular mode of operation, can be clearlyrecognized and evaluated when the detector of a programming unit isformed in such a way that, in addition to the ranges of detection forthe various differing modes of operation, it includes at least oneadditional range of detection for a switching signal which differs fromthe switching signals in the operating positions of the operatingswitch.

Whereas the detector of the known device according to the Germanspecification No. DE OS 2,944,224 only includes a number of ranges ofdetection which corresponds to the number of possible modes of operationor operating positions of the operating switch the number of detectionranges of the detector according to the present invention is increased.Furthermore, the invention provides for measuring a voltage level on theswitching signal transmission path, lies outside the ranges of detectionof the voltage levels adjusted in desired modes of operation. Thus theprogramming unit with the detector can clearly distinguish abnormal fromnormal operation and then release appropriate control signals which forexample can switch off the entire system.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention and its advantages developments are described below indetail by way of the embodiments shown in the accompanying drawing, inwhich:

FIG. 1 is a circuit diagram of a first circuit arrangement for awindshield cleaning system,

FIG. 2 is a circuit diagram of a detector,

FIG. 3 is a circuit diagram of a second embodiment of a circuitarrangement for a windshield cleaning system and

FIG. 4 is a circuit diagram of a third embodiment of a circuitarrangement for a windshield cleaning system.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

FIG. 1 shows the circuit diagram for a windshield cleaning system of amotor vehicle. Part of this circuit arrangement is an operating switch10 with a mechanically adjustable contact bridge 11 for determiningdifferent modes of operation of the windshield cleaning system. Thiscontact bridge 11 is continuously connected with the first pole 12 of avoltage source, not shown in detail, which pole is also connected withthe body of the motor vehicle. In the various operating positions a-hthe contact bridge 11 effects an electrically conductive connectionbetween the pole 12 of a voltage source and one of the stationarycontacts 13. The neutral position of the operating switch 10 is shown inFIG. 1. Upon adjustment of the contact bridge 11 to the left-hand side,as viewed in FIG. 1, into the operating positions b to f intermittentoperation of the windshield cleaning system is switched on. Eachposition represents a different interval time. In the operating positiong continuous operation with a low wiper speed is activated and in theoperating position h continuous operation with a high wiper speed isactivated. In the neutral position a the mode of operation "parkingposition run" is switch on. This position the wiper runs to its parkingposition and is switched off thereafter. In addition, an operatingposition g' is provided to the extreme right-hand side of the neutralposition, as shown in the drawing in which position g' the so-calledtip-wiping-operation is to be switched on. Only for completeness's sakeit is pointed out herein that the operating switch 10 also includes awasher key 15 by way of which a particular mode of operation of thewindshield wiper system is switched along with the washer system.

From FIG. 1 it can be seen that several stationary contacts 13 are eachconnected with the same output 17, 18 or 19 of the operating switch byway of resistors each having different values. Thus in each of theoperating positions a, b, c there is effected an electrically conductiveconnection between one pole 12 of the voltage source and one of theresistors 20a, 20b or 20c with the output 17. In the operating positionsd, e, f one of the resistors 21 is accordingly connected to the output18. In the operating positions g, h one of the resistors 22b, 22c isconnected with the output 19 and upon operation of the washer key 15 aresistor 22a is also connected with this output 19. The resistors 20a,21a and 22a have the same resistance values. However, the threeresistors 20a, 20b and 20c connected to one output have differentresistance values in approximately a ratio of 1 to 3 to 90.

From the circuit diagram according to FIG. 1 it can also be seen thateach of the outputs 17, 18, 19 is connected with the pole 12 of thevoltage source by way of an associated resistor 25. The associatedoutput is held on a particular voltage level by way of this resistor 25,when the contact bridge 11 of the operating switch is not in contactwith a stationary contact 13.

It can also be seen from the circuit diagram that in the operatingpositions g or g' the same resistor 22b is connected into the circuit.Thus, these operating positions are of equal value electrically, butdiffer mechanically in that the contact bridge 11 is locked in theoperating position g, but it is not locked in the operating position g'.The contact bridge 11 rather springs back automatically from theoperating position g' into the neutral position a. Thus, coded switchingsignals may be tapped off at the outputs of the operating switch, whichswitching signals differ with regard to the voltage level as far as thepresent embodiment is concerned.

Part of the circuit arrangement is a programming unit designatedgenerally as 30 with a detector 31, which responds to differently codedswitching signals of the operating switch and determines the associatedmode of operation. The detector 31 is integrated in a microprocessor 32or a custom-designed chip. The three inputs 37, 38 and 39 of theprogramming unit are each connected with the other pole 41 of thevoltage source by way of separate resistors 40. Three protectiveresistors 42 also provided.

The operating switch 10 is connected with the programming unit 30 by wayof three switching signal transmission paths 47, 48 and 49. In thesimplest case, electric leads can serve as switching signal transmissionpaths, however the switching signals of the operating switch might alsobe transmitted optically or acoustically. Thus, it can be seen from thecircuit diagram according to FIG. 1 that the number of switching signaltransmission paths is less than the number of possible operatingpositions of the operating switch. In the embodiment according to FIG. 1three switching signal transmission paths are provided for a total ofnine different modes of operation.

In the circuit diagram according to FIG. 1 the wiper motor of a wipersystem forms an electrical load designated 50, to which wiper motor aso-called parking position switch 51 is associated. The wiper motor 50is alternately connected with one or other pole of a voltage source byway of the relay 52. Another relay 53 determines whether the wipersystem is to be operated with the lower or higher wiper speed. Thiscircuit arrangement for controlling the wiper motor 50 is known and,therefore, need not to be described in detail. FIG. 1 furthermore showsa further load 55, namely a washing pump motor controlled by a relay 56.Dependent on the operating position of the operating switch 10 or on thevoltage levels at the inputs 37, 38, 39 the programming unit 30 effectsthe appropriate mode of operation of the load 50 whether the load 55 tobe switched on. For this purpose, control signals for the various relays52, 53, 56 are released at particular points of time in a known manner.

The detector 31, whose circuit diagram is shown in FIG. 2, therebyserves to determine the modes of operation. The detector includesseveral comparators 60, 61 or 62. The comparators 60a, 60b, 60c, 60d,60e and 60f are all connected to the input 37 and thus are controlled bythe voltage level on the switching signal transmission path 47 or on theoutput 17 of the operating switch 10, respectively. The comparators 61are all connected with the input 38 and the comparators 62 with theinput 39. Each of these comparators acts in a given range of detection.For example, a signal may be measured at the output of the comparator60d, when the voltage level at the input 37 lies in the range of 0 voltor a ratio of 0% of the voltage of the voltage source. The comparator60e responds when the voltage level lies in the ratio of 20% of thesupply voltage. Correspondingly, the comparators 60a60b, 60c and 60frelease a switching signal, if the voltage level lies in the range of40%, 60%, 80%, 100% of the supply voltage. The same applies for thecomparators 61 and 62. These type of signal-recognition comparators arealso designated window discriminators.

In the circuit diagram according to FIG. 2 the operating switch 10 hasalso been indicated. Two different operating positions of the contactbridge 11 can be seen therein which, of course, cannot be simultaneouslyswitch on. When the contact bridge 11 rests upon one of the stationarycontacts 13, a voltage level is to be measured at the input 37 of theprogramming unit 30 in such a way that one of the comparators 60a, 60band 60c responds. This is achieved by an appropriate dimensioning of theresistors 20, 25 and 40. Thus, in the operating position a, thecomparator 60a is to respond, in the operating position b, thecomparator 60b and in the operating position c, the comparator 60c. Therespective mode of operation, in the present case the interval timeduring intermittent operation, is then determined by the outputs ofthese comparators. Thus one can see from FIG. 2 that the detector 31 hasthree ranges of detection Da, Db, Dc, which are associated withparticular modes of operation which may be predetermined by way of theassigned operating switch and the switching signal transmission path 47respectively. It is essential for the present invention that, inaddition to the ranges of detection associated with the various modes ofoperation, the detector has three further ranges of detection Dd, De, Dfwhich respond to switching signals not representative of any desiredmode of operation.

If the contact bridge 11 is located between two operating positions,thus between the operating positions e and f, the voltage divider at theinput 38 changes, because now none of the resistors 20, 21 or 22associated with the stationary contact 13 is connected to the circuit.Thus, in this case, none of the comparators 61a, 61b, 61c associatedwith the various modes of operation respond, but rather the comparator61e is to respond. Thus, the detector 31 has a first additional range ofdetection De for a switching signal or a voltage level at its input,which signal or voltage level differs from the customary switchingsignals or voltage levels in the operating positions of the operatingswitch 10. This additional first range of detection comprises switchingsignals having a voltage level of about 20% of the supply voltage.

Troubles can also appear in a circuit arrngement of this kind, becausethe switching signal transmission path to an input 39 might beinterrupted. Thus, in his case, the full positive supply voltage will beconnected to the input by way of the resistor 40 and, consequently, thecomparator 62f will respond. Thus, the detector 31 has a secondadditional range of detection Df for a voltage level differing from thenormal voltage levels in one of the modes of operation. Theoretically,it could also happen that the switching signal transmission path bedirectly connected with the positive pole of the voltage source. Also,in this case, the full supply voltage is connected to the input 39 andthe comparator 62f is again to respond. Thus, this second additionalrange of detection Df of the detector 31 serves to detect two faultyconditions.

However, a short-circuit with regard to the negative pole of the voltagesource will appear more often. In that case no voltage is switched ontothe input 39 and the comparator 60d responds. Thus, there is obtained afurther additional range of detection Dd laid for recognizing anothertrouble situation.

Thus, the number of the ranges of detection of the detector is greaterthan the number of the different modes of operation provided. In theembodiment represented in the drawing there are three ranges ofdetection for each switching signal transmission path in predeterminedmodes of operation and three additional ranges of detection. In twoadditional ranges of detection Dd, Df troubles are detected, namely anopen switching signal transmission path or short-circuits with thepositive or negative poles of the voltage source. In a furtheradditional range of detection De it is detected whether the contactbridge is positioned between two operating positions. This applies toeach switching signal transmission path of the preferred embodiment,wherein the output signals of equally acting comparators areinterrelated by means of an OR-gate 65a, b, c. The output signal ofthese OR-gates can be used for a control in different ways. In a case oftrouble, for example when there is a short-circuit or the switchingsignal transmission path is open, the entire system can be switched offin a delayed manner by a timing element 63. A signal appears at theoutput of the OR-gate 65b when the switch contact 11 is located betweentwo operating positions. In this situation the current mode of operationis to be retained, so long as the duration of the switching signal doesnot exceed a given time. If the switching signal with a voltage levelcorresponding to the range of detection detected by the comparator 20e,21e, 22e is longer than a predetermined time, the switch will mostlikely be defective and the system can be switched off.

In the embodiment according to FIGS. 1 and 2 six different voltagelevels may be transmitted on each switching signal transmission path andmonitored by the following comparators. Three of the comparators areassociated with the normal modes of operation, whereas three furthercomparators are associated with the additional ranges of detection.

In the embodiment according to FIG. 3 there are also on each switchingsignal transmission path six different voltage levels to be transmittedand monitored by comparators, however, in order to minimize switchingsignal transmission paths, four different voltage levels are associatedwith different modes of operation, whereas only two other voltage levelslie within the additional ranges of detection. This can be seen from thedrawing by the fact that four each of the stationary contacts 13 areconnected with an output 18 or 19 by way of associated resistors 21, 22.These resistors are selected in such a way that in the predeterminedmodes of operation 20%, 40%, 60% or 80% of the supply voltage areapplied to the input 38 or 39 of the programming unit 30. Thus, in thisembodiment only two additional ranges of detection Dd, Df for voltagelevels of 0% or 100% of the supply voltage are possible. In thisembodiment the resistors 25 by way of which the voltage level of theembodiment according to FIG. 1 is determined when the switch is open arenot used. Consequently, the same voltage level may be measured in theembodiment according to FIG. 3 when the contact bridge 11 is positionedbetween two operating positions or when the switching signaltransmission path 48, 49 is interrupted or short-circuited with thepositive pole 41 of the voltage source. It is however possible todistinguish the two conditions easily, because, during the changeover ofthe operating switch, this signal is only applied for a short time, butit can be measured over a longer period of time for example when thelead is interrupted or when there is a short-circuit. Consequently, thisprogramming unit will be designed in such a way that the duration of aswitching signal lying within this additional range of detection Df isalso evaluated and different control signals are released in dependenceon the duration. If this switching signal is only applied for arelatively short time, the current mode of operating is retained.However, the system is switched off with a longer duration of aswitching pulse within this additional range of detection Df.

Furthermore one can see from FIG. 3 that, upon actuation of the washerkey 15, a voltage level may be measured at the output 18, which voltagelevel corresponds to the voltage level in the case of a short-circuitwith one pole 12. Because it can be assumed that the washing pump motor5 is only controlled for a short time by this washer key, the sameprinciple of additionally monitoring the duration of the switchingsignal can be applied. If the switching signal within this additionalrange of detection Dd provided for a short-circuit lasts only for ashort time, the mode of operation "washing" will be switched on. If, incontrast thereto, the duration is long, the system will be switched off.

Thus, in addition to the ranges of detection for the various differentmodes of operation, the detector of the embodiment according to FIG. 3has two additional ranges of detection for switching signals differingfrom switching signals in the operating positions of the operatingswitch. Thus, operational reliability is also ensured for thisembodiment. In addition, this embodiment also has the advantage of a lownumber of leads required between the operating switch and theprogramming unit.

In the embodiment of FIG. 4 the operating switch 10 has two contactbridges 11 and 11' which are jointly adjusted and which thereafterswitch different voltage levels onto the two switching signaltransmission paths 47 and 48 by way of resistors. The resistorsassociated with the switch can be selected in such a way that, startingfrom the rest position shown, with an adjustment to the left-hand side,as viewed in FIG. 4 voltage levels of 40%, 40% 40%, 60%, 60%, 50%, 80%,80% and 80% of the supply voltage are successively switched onto theswitching signal transmission path 48, whereas at the same time voltagelevels of 40%, 60% 80%, 40%, 40%, 80%, 40%, 60%, 80% of the supplyvoltage are switched onto the switching signal transmission path 47 byway of the contact bridge 11'. Upon transition from one operatingposition into the successive one, a voltage level of 20% of the supplyvoltage may be measured on both switching signal transmission paths.

Due to the voltage level at its inputs 37, 38, the detector determinesthe mode of operation for a load. If a voltage level of 40%, isavailable on one input 38 and at the other input 37 a voltage level of40% intermittent operation is, for example, to be switched on. If,however, at both inputs 37 and 38 a voltage level of 80% of the supplyvoltage is applied, continuous operation with high wiper speed is to beswitched on. The detector thus detects the mode of operation fromseveral simultaneously applied voltage levels whose level depends on theoperating position of the operating switch.

Thus, this embodiment clearly shows that nine different modes ofoperation or operating positions of the operating switch and furtheradditional switching signals representing system troubles can berecognized with only two switching signal transmission paths.

This design is especially favourable in regard to costs and can beeffected with a small number of switching signal transmission paths fora plurality of predetermined modes of operation, even if faultyconditions are not to be evaluated.

The present invention has been described by way of an embodimentsrelating to a windshield wiper system for motor vehicles. Of course, thebasic ideas can also be applied for the control of other electricalloads in a motor vehicle. However, in each one of the embodimentsdescribed there are provided several leads between the operating switchand the programming unit. Thus, the principle of the invention is alsoapplicable, if all switching signals of the operating switch are to betransmitted over a single lead. The principle of the invention has beenillustrated by way of examples in which the switching signalsdistinguish by different voltage levels. However, the basic idea canalso be advantageously used, if the switching signals differ in othercriteria, for example with regard to frequency or pulse duration. Evenif the switching signals released by the operating switch have a digitalcoding the basic idea of the invention can be realized, although in thiscase, e.g., with the use of a Gray code the problem of a non-definedswitching signal during a changeover of the operating switch from oneposition to the other does not appear. In the embodiments described thecontact bridge of the operating switch always has one side connected toground and thus to that pole of the voltage source to which the body ofthe motor vehicle is connected. Thus, the contact bridge might inprinciple also be connected with the positive pole of the voltagesource, but in that case the resistors with a relatively low resistancein the operating switch would have to endure a relatively high powerdissipation when a short-circuit of the switching signal transmissionpath to ground occurs.

Finally it is also pointed out that the control signals released in thecases of trouble can be evaluated quite differently. Either the entiresystem can be switched off or only that switching signal transmissionpath on which the switching signal characterizing a trouble has beenmeasured can be interrupted. Of course, a trouble might also beindicated acoustically or optically in order to leave it to the user'sdecision how to react to a particular trouble.

In order to ensure that, in this analogous processing of measured valuesvoltage swings do not affect the measured result, in most cases astabilized voltage source will be used or the resistors will be suppliedwith a constant current. However, in a particularly simple example, theresistors and the comparators may also be directly connected with thebattery of the motor vehicle. Upon voltage swings, both the voltagelevel to be evaluated and the range of detection of a comparator changewithout adverse effects upon the evaluation, insofar as these ranges ofdetection differ sufficiently from each other.

The entire system is preferably be built up in integrated manner, byusing appropriately programmed microprocessors or microcomputers orcustom-designed chips.

What is claimed is:
 1. A circuit arrangement for at least one electricaccessory load of a motor vehicle of the type for a windshield cleaningsystem, comprising an operating switch switchable into several differentoperating positions in order to determine different modes of operation,means for programming including detector means for responding todifferent switching signals from the operating switch and, said detectormeans determining an associated mode of operation of the load when theswitching signal lies within a particular range of detection, aplurality of switching signal transmission paths between the operatingswitch and said detector means, the number of signal transmission pathsbeing less than the number of possible operating positions of theoperating switch wherein, in addition to the ranges of detection fordetecting the various modes of operation, the detector means includes atleast one additional range of detection for detecting a switching signalwhich differs from the switching signal in each of the differentoperating positions of the switch and wherein said operating switchincludes a contact bridge interconnected with said means forprogramming.
 2. The circuit arrangement according to claim 1 whereinsaid detector means detects different operating voltage levels on atleast one of said switching signal transmission paths in the variousoperating positions, each operating voltage level representing anassigned range of detection of the detector.
 3. The circuit arrangementaccording to claim 2 wherein during changeover of the operating switchfrom one operating position into a different operating position, a firstsignal voltage level is switched onto the switching signal transmissionpath, said first signal voltage level differs from the operating voltagelevels in each of the operating positions, said first signal voltagelevel representing a first additional range of detection.
 4. The circuitarrangement according to claim 3 wherein said detector means retains themode of operation defined by said one operating position for a definedperiod of time when said first signal voltage is within said firstadditional range of detection.
 5. A circuit arrangement for at least oneelectric accessory load of a motor vehicle of the type for a windshieldcleaning system, comprising an operating switch switchable into severaldifferent operating positions in order to determine different modes ofoperation, a programming unit including detector means for responding todifferent switching signals from the operating switch and, said detectormeans determining an associated mode of operation of the load when theswitching signal lies within a particular range of detection, a numberof switching signal transmission paths between the operating switch andsaid detector means, the number of signal transmission paths being lessthan the number of possible operating positions of the operating switchwherein, in addition to the ranges of detection for detecting thevarious modes of operation, the detector means includes at least oneadditional range of detection for detecting a switching signal whichdiffers from the switching signal in each of the different operatingpositions of the operating switch, wherein said detector means detectsdifferent operating voltage levels on at least one of said switchingsignal transmission paths in the various operating positions, eachoperating voltage level representing an assigned range of detection ofthe detector, wherein during changeover of the operating position, afirst signal voltage level is switched onto the switching signaltransmission path, said first signal voltage level differs from theoperating voltage levels in each of the operating positions, said firstsignal voltage level representing a first additional range of detection,and wherein upon a short-circuit of a signal transmission path with onepole of a voltage source for the load, a second signal voltage level isapplied to the switching signal transmission path, said second signalvoltage differs from the operating voltage levels in each of theoperating positions, said second signal voltage level is associated withat least a second additional range of detection.
 6. The circuitarrangement according to claim 5 wherein upon a short-circuit of aswitching signal transmission path with the positive pole of the voltagesource the second signal voltage level lies within the second additionalrange of detection, and upon a short-circuit with the negative pole ofthe voltage source the second signal voltage level lies within a thirdadditional range of detection.
 7. The circuit arrangement according toclaim 6 wherein when the switching signal transmission path isinterrupted, a third signal voltage level different from the operatingvoltage levels in the operating positions is applied to the switchingsignal transmission path said third signal voltage level is associatedwith a fourth additional range of detection.
 8. The circuit arrangementaccording to claim 7 wherein the second additional range of detectionprovided for the short-circuit is equal to the fourth additional rangeof detection for the third signal voltage level available withinterrupted switching signal transmission path.
 9. The circuitarrangement according to claim 6 including means for switching off thevoltage source to all loads upon detection of the second signal voltagecorresponding to the second or third range of detection.
 10. The circuitarrangement according to claim 6 including means for switching off atleast one mode of operation of at least one load upon detection of thesecond signal voltage within the second or third additional range ofdetection.
 11. A circuit arrangement for at least one electric accessoryload of a motor vehicle of the type for a windshield cleaning system,comprising an operating switch switchable into several differentoperating position sin order to determine different modes of operation,a programming unit including detector means for responding to differentswitching signals from the operating switch and, said detector meansdetermining an associated mode of operation of the load when theswitching signal lies within a particular range of detection, a numberof switching signal transmission paths between the operating switch andsaid detector means, the number of signal transmission paths being lessthan the number of possible operating positions of the operating switchwherein, in addition to the ranges of detection for detecting thevarious modes of operation, the detector means includes at least oneadditional range of detection for detecting a switching signal whichdiffers form the switching signal in each of the different operatingpositions of the operating switch, wherein the operating switch has acontact bridge which changes over into different operating positions,said contact bridge connected with a first pole of a voltage source and,in each of the different operating positions, rests upon one of aplurality of stationary contacts, each of said plurality of stationarycontacts connected with one output of the operating switch byway offirst resistors, each first resistor having a different resistancevalue, an output from each of the first resistors connected withseparate inputs to the programming unit by way of a switching signaltransmission path, each input to the programming unit connected with asecond pole of the voltage source by way of second resistors, andwherein the outputs of the operating switch are each connected with thefirst pole by way of a third resistor.
 12. The circuit arrangementaccording to claim 11 wherein the resistance values of the variousresistors are provided such that upon a short-circuit of a switchingsignal transmission path with the first pole of the voltage source avoltage level of 0% relative to the voltage source may be measured atthe input of the programming unit, upon a short-circuit with the secondpole of a voltage source, a voltage level of 100% relative to thevoltage source, during changeover from one operating position intoanother, a voltage level of 20% relative to the voltage source and inthe operating positions a voltage level greater than 20% and smallerthan 100% relative to the voltage source.
 13. The circuit arrangementaccording to claim 11 wherein the first pole of the voltage source isalso connected to the body of the motor vehicle.
 14. The circuitarrangement according to claim 11 wherein the detector also evaluatesthe duration of at least one signal voltage lying within at least oneadditional range of detection and, in dependence on the duration,generates different control signals.
 15. The circuit arrangementaccording to claim 14 wherein during changeover of the operating switchfrom one operating position into another position and when the switchingsignal transmission path is interrupted, a first signal voltage leveldiffering from the operating voltage levels in the operating positionsis detected, said first signal voltage level is associated with a firstadditional range of detection, the mode of operation being retained fora first signal voltage duration lasting less than a predetermined timeand said mode of operation switched off for a first signal voltageduration lasting longer than said predetermined time.
 16. The circuitarrangement according to claim 15 wherein a second signal voltage leveloccurring during a short-circuit of the switching signal transmissionpath with one pole of the voltage source corresponds to a voltage leveloccurring during switching-on of a particular load, said second signalvoltage level is associated with all electric loads being retained for aduration of the second signal voltage level less than a predeterminedtime and all loads being switched off for a duration of said secondsignal voltage level lasting longer than said predetermined time. 17.The circuit arrangement according to claim 11 wherein the operatingswitch has a plurality of contact bridges adapted to switch whichdifferent voltage levels onto a plurality of switching signaltransmission paths, said detector determining a particular mode ofoperation of said load from said different voltage levels, said voltagelevels being simultaneously measured.